Microsatellite markers in avocado (Persea americana Mill.): genealogical relationships among cultivated avocado genotypes

Twenty-five microsatellite markers uniquely differentiated 35 avocado cultivars and two wild relatives. Average heterozygosity was high (60.7%), ranging from 32% in P. steyermarkii to 84% in Fuerte and Bacon. In a subset of 15 cultivars, heterozygosity averaged 63.5% for microsatellites, compared to 41.8% for restriction fragment length polymorphisms (RFLPs). A neighbor-joining tree, according to average shared allele distances, consisted of three clusters likely corresponding to the botanical races of avocado and intermediate clusters uniting genotypes of presumably racially hybrid origin. Several results were at odds with existing botanical assignments that are sometimes rendered difficult by incomplete pedigree information, the complexity of the hybrid status (multiple backcrossing), or both. For example, cv. Harvest clustered with the Guatemalan race cultivars, yet it is derived from the Guatemalan x Mexican hybrid cv. Gwen. Persea schiedeana grouped with cv. Bacon. The rootstock G875 emerged as the most divergent genotype in our data set. Considerable diversity was found particularly among accessions from Guatemala, including G810 (West Indian race), G6 (Mexican race), G755A (hybrid Guatemalan x P. schiedeana), and G875 (probably not P. americana). Low bootstrap support, even upon exclusion of (known) hybrid genotypes from the data matrix, suggests the existence of ancient hybridization or that the botanical races originated more recently than previously thought.     

Molecular characterization of avocado germplasm with a new set of SSR and EST-SSR markers: genetic diversity, population structure, and identification of race-specific markers in a group of cultivated genotypes

Although molecular characterization of the avocado germplasm started with the early development of molecular markers, the genetic relationships among the three botanical races are still uncertain. Here, we report the development of 47 new microsatellites in avocado (Persea americana Mill) and the results of various genetic studies carefully designed to address the unsolved questions. Forty high-quality, single-locus markers (25 simple sequence repeats (SSRs) and 15 expressed sequence tag–SSRs (EST-SSRs)) were evaluated in a selected group of 42 cultivated accessions, which represent the three described botanical races. A total of 455 alleles (11.4 alleles per locus) have been detected. The mean expected and observed heterozygosities averaged 0.831 and 0.674, respectively. All the analyzed genotypes could be unequivocally distinguished with an accumulated probability of identity value of 6.36?×?10^?50. Seventy-five percent of the loci showed a significant departure from Hardy–Weinberg equilibrium, most likely due to the substructure of the accession set and kinship among some of the accessions. The genetic relationships among the accessions were explored using different methods. We demonstrate that the correct allocation of the avocado cultivars requires the complementary use of distance-based and model-based methods. All of the results agreed with the existence of three groups to which accessions were assigned based on their botanical race, with 25 % of the detected variation being partitioned among the groups. The diversity analysis within each group has allowed for the identification of unique alleles that are useful as race-specific markers. The effects of the different experimental parameters on the results are discussed.     

The SSR-based molecular profile of 1005 grapevine (Vitis vinifera L.) accessions uncovers new synonymy and parentages, and reveals a large admixture amongst varieties of different geographic origin

A collection of 1005 grapevine accessions was genotyped at 34 microsatellite loci (SSR) with the aim of analysing genetic diversity and exploring parentages. The comparison of molecular profiles revealed 200 groups of synonymy. The removal of perfect synonyms reduced the database to 745 unique genotypes, on which population genetic parameters were calculated. The analysis of kinship uncovered 74 complete pedigrees, with both parents identified. Many of these parentages were not previously known and are of considerable historical interest, e.g. Chenin blanc (Sauvignon × Traminer rot), Covè (Harslevelu selfed), Incrocio Manzoni 2–14 and 2–15 (Cabernet franc × Prosecco), Lagrein (Schiava gentile × Teroldego), Malvasia nera of Bolzano (Perera × Schiava gentile), Manzoni moscato (Raboso veronese × Moscato d’Amburgo), Moscato violetto (Moscato bianco × Duraguzza), Muscat of Alexandria (Muscat blanc à petit grain × Axina de tres bias) and others. Statistical robustness of unexpected pedigrees was reinforced with the analysis of an additional 7–30 SSRs. Grouping the accessions by profile resulted in a weak correlation with their geographical origin and/or current area of cultivation, revealing a large admixture of local varieties with those most widely cultivated, as a result of ancient commerce and population flow. The SSRs with tri- to penta-nucleotide repeats adopted for the present study showed a great capacity for discriminating amongst accessions, with probabilities of identity by chance as low as 1.45 × 10^?27 and 9.35 × 10^?12 for unrelated and full sib individuals, respectively. A database of allele frequencies and SSR profiles of 32 reference cultivars are provided.     

Assessment of molecular diversity and evolutionary relationship of kenaf (Hibiscus cannabinus L.), roselle (H. sabdariffa L.) and their wild relatives

Kenaf (Hibiscus cannabinus L.) and roselle (H. sabdariffa L.) are valuable fibre crop species with diverse end use. Phylogenetic relationship of 73 accessions of kenaf, roselle and their wild relatives from 15 countries was assessed using 44 inter-simple sequence repeat (ISSR) and jute (Corchorus olitorius L.) specific simple sequence repeats (SSR) markers. A total of 113 alleles were identified of which 61.95 % were polymorphic. Jute specific SSR markers exhibited high polymorphism and resolving power in kenaf, although ISSR markers exhibited higher resolving power than SSR markers. Number of polymorphic alleles varied from 1 to 5 for ISSR and 1 to 6 for SSR markers. Cultivated species exhibited higher allele polymorphism (57 %) than the wild species (35 %), but the improved cultivars exhibited lower genetic diversity compared to germplasm accessions. Accessions with common genetic lineage and geographical distribution clustered together. Indian kenaf varieties were distinct from cultivars bred in other countries and shared more genetic homology with African accessions. High genetic diversity was observed in the Indian (J = 0.35–0.74) and exotic kenaf germplasm collections (J = 0.38–0.79), suggesting kenaf might have been introduced in India from Africa through Central Asia during early domestication. Genetic similarity-based cluster analysis was in close accordance with taxonomic classification of Hibiscus.     

Intercontinental variation of Sclerospora graminicola

Collections of S. graminicola were made from local pearl millet crops in West Africa and India. Asexual inoculum was derived from the collections in Polythene tunnels and used to infect pearl millet cultivars from both continents. Analysis of deviance of the incidence of disease was performed on the logit scale using GLIM. The host × pathogen interactions were interpreted by use of the Finlay-Wilkinson regression technique widely used in the study of genotype × environment interactions. While the West African collections were consistently more pathogenic than the Indian ones, West African hosts were potentially more susceptible to Indian than to West African pathogen isolates; conversely some Indian hosts were more vulnerable to West African than to Indian isolates. There was a fairly stable relationship between incidence of disease and relative pathogenicity of West African isolates but the Indian isolates were more variable in their susceptibility to changing background levels of disease. These results could influence resistance breeding strategies in pearl millet improvement programmes. The methods of analysis could be valuable for application to other complex and ill-defined pathosystems.     

SSR and morphological trait based population structure analysis of 130 diverse flax (Linum usitatissimum L.) accessions

A total of 130 flax accessions of diverse morphotypes and worldwide origin were assessed for genetic diversity and population structure using 11 morphological traits and microsatellite markers (15 gSSRs and 7 EST–SSRs). Analysis performed after classifying these accessions on the basis of plant height, branching pattern, seed size, Indian/foreign origin into six categories called sub-populations viz. fibre type exotic, fibre type indigenous, intermediate type exotic, intermediate type indigenous, linseed type exotic and linseed type indigenous. The study assessed different diversity indices, AMOVA, population structure and included a principal coordinate analysis based on different marker systems. The highest diversity was exhibited by gSSR markers (SI = 0.46; He = 0.31; P = 85.11). AMOVA based on all markers explained significant difference among fibre type, intermediate type and linseed type populations of flax. In terms of variation explained by different markers, EST-SSR markers (12%) better differentiated flax populations compared to morphological (9%) and gSSR (6%) markers at P = 0.01. The maximum Nei's unbiased genetic distance (D = 0.11) was observed between fibre type and linseed type exotic sub-populations based on EST-SSR markers. The combined structure analysis by using all markers grouped Indian fibre type accessions (63.4%) in a separate cluster along with the Indian intermediate type (48.7%), whereas Indian accessions (82.16%) of linseed type constituted an independent cluster. These findings were supported by the results of the principal coordinate analysis. Morphological markers employed in the study found complementary with microsatellite based markers in deciphering genetic diversity and population structure of the flax germplasm.     

ISOZYMATIC VARIATION IN GUATEMALAN RACES OF MAIZE

Isozymatic data taken from 67 Guatemalan collections of maize were subjected to numerical taxonomic analyses to elucidate systematic relationships among the 19 maize races and subraces described for Guatemala by Wellhausen et al. As with Bolivian and Mexican races, isozymatic variation in Guatemalan maize was strongly associated with altitude. Guatemalan lowland races were in general isozymatically distinct from races of higher elevations. Two middle elevation Guatemalan races proved difficult to place taxonomically. As a group, Guatemalan highland races were isozymatically more diverse than races from lower elevations, and were rather weakly differentiated from Mexican highland races. Notably, variational patterns evident from phenetic analyses of isozyme data were generally congruent with those apparent in phylogenetic analyses. The data reported here, and in earlier studies, suggested that divergent combinations of isozymatic, karyotypic, and morphological features have evolved in local maize races from Mexico, Guatemala, and Bolivia, perhaps as the result of the different selective regimens indigenous cultivators have imposed on different regional phylogenetic lineages.     

Molecular genetic diversity and association mapping of nut and kernel traits in Slovenian hazelnut (<Emphasis Type="Italic">Corylus avellana</Emphasis>) germplasm

European hazelnut (Corylus avellana L.), cultivated in several areas of the world including Europe, Anatolia, and the USA, is an economically important nut crop due to its high mineral, oleic acid, amino acid, and phenolic compound content and pleasant flavor. This study examined molecular genetic diversity and population structure of 54 wild accessions and 48 cultivars from the Slovenian national hazelnut collection using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers. Eleven AFLP primer combinations and 49 SSR markers yielded 532 and 504 polymorphic fragments, respectively. As expected for a wind-pollinated, self-incompatible species, levels of genetic diversity were high with cultivars and wild accessions having mean dissimilarity values of 0.50 and 0.60, respectively. In general, cultivars and wild accessions clustered separately in dendrogram, principal coordinate, and population structure analyses with regional clustering of the wild material. The accessions were also characterized for ten nut and seven kernel traits and some wild accessions were shown to have breeding potential. Morphological principal component analysis showed distinct clustering of cultivars and wild accessions. An association mapping panel composed of 64 hazelnut cultivars and wild accessions had considerable variation for the nut and kernel quality traits. Morphological and molecular data were associated to identify markers controlling the traits. In all, 49 SSR markers were significantly associated with nut and kernel traits [P < 0.0001 and LD value (r ²) = 0.15–0.50]. This work is the first use of association mapping in hazelnut and has identified molecular markers associated with important quality parameters in this important nut crop.     

Development and characterization of microsatellite markers in Indian sesame (Sesamum indicum L.)

The genetic characterization of Indian sesame cultivars and related wild species was analysed using 102 simple sequence repeat (SSR; microsatellite) markers. Of these, 62 were novel sesame-specific microsatellites isolated in the course of the present investigation by constructing genomic libraries. Characterization of the 68 sesame accessions and three related wild species using 72 polymorphic SSR primers resulted in the detection of 170 alleles. The number of alleles ranged from two to four with an average of 2.5 alleles per locus. Polymorphic information content of the markers ranged from 0.43 to 0.88 with an average of 0.66. UPGMA cluster analysis grouped all the accessions into two major clusters with a genetic similarity ranging from 0.40 to 0.91. A moderate to high level of genetic variability was observed. The three wild accessions used in the study formed separate clades and distant genetic relationships were observed between the cultivar lines and wild species. Differentiation of genotypes according to geographical region was not observed. Analysis of molecular variance (AMOVA) analysis revealed that a high percentage of variation was within populations (87.1 %). An overall F _st of 0.11 among the populations indicated low population differentiation. The SSR markers developed will be useful for further genetic analysis, linkage mapping and selection of parents in future breeding programmes.     

Gene-environment interactions and obesity traits among postmenopausal African-American and Hispanic women in the Women’s Health Initiative SHARe Study

Genome-wide association studies (GWAS) of obesity measures have identified associations with single nucleotide polymorphisms (SNPs). However, no large-scale evaluation of gene-environment interactions has been performed. We conducted a search of gene-environment (G × E) interactions in post-menopausal African-American and Hispanic women from the Women’s Health Initiative SNP Health Association Resource GWAS study. Single SNP linear regression on body mass index (BMI) and waist-to-hip circumference ratio (WHR) adjusted for multidimensional-scaling-derived axes of ancestry and age was run in race-stratified data with 871,512 SNPs available from African-Americans (N = 8,203) and 786,776 SNPs from Hispanics (N = 3,484). Tests of G × E interaction at all SNPs for recreational physical activity (m h/week), dietary energy intake (kcal/day), alcohol intake (categorical), cigarette smoking years, and cigarette smoking (ever vs. never) were run in African-Americans and Hispanics adjusted for ancestry and age at interview, followed by meta-analysis of G × E interaction terms. The strongest evidence for concordant G × E interactions in African-Americans and Hispanics was for smoking and marker rs10133840 (Q statistic P = 0.70, beta = ?0.01, P = 3.81 × 10^?7) with BMI as the outcome. The strongest evidence for G × E interaction within a cohort was in African-Americans with WHR as outcome for dietary energy intake and rs9557704 (SNP × kcal = ?0.04, P = 2.17 × 10^?7). No results exceeded the Bonferroni-corrected statistical significance threshold.     

Linkage Mapping and Molecular Diversity at the Flower Sex Locus in Wild and Cultivated Grapevine Reveal a Prominent SSR Haplotype in Hermaphrodite Plants

Cultivars used for wine and table grape have self-fertile hermaphrodite flowers whereas wild European vines and American and Asian species are dioecious, having either male or female flowers. Consistent with previous studies, the flower sex trait was mapped as a single major locus on chromosome 2 based on a pure Vitis vinifera population segregating for hermaphrodite and female progeny, and a hybrid population producing all three flower sex types. The sex locus was placed between the same SSR and SNP markers on both genetic maps, although abnormal segregation hampered to fine map the genomic region. From a total of 55 possible haplotypes inferred for three SSR markers around the sex locus, in a population of 132 V. sylvestris accessions and 171 V. vinifera cultivars, one of them accounted for 66 % of the hermaphrodite individuals and may be the result of domestication. Specific size variants of the VVIB23 microsatellite sequence within the 3′-UTR of a putative YABBY1 gene were found to be statistically significantly associated with the sex alleles M, H and f; these markers can provide assistance in defining the status of wild grapevine germplasm.     

Activities of photosystem II and antioxidant enzymes in chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) cultivars exposed to chilling temperatures

This study was carried out to determine the effect of chilling on both cold-acclimated and non-acclimated chickpea (Cicer arietinum L.) cultivars (Gökçe and Can?tez 87). Chickpea seedlings grown in soil culture for 12 days were subjected to chilling temperatures (2 and 4°C for 12 days) after maintaining in cold-acclimation (10°C, 7 days) or non-acclimation (25°C, 7 days) periods. The lowest values of growth parameters were obtained with cold-acclimated plants, whereas non-acclimated plants exhibited the lowest water content values, especially at 2°C. There was no effect of cold-acclimation period on chlorophyll fluorescence parameters. Plants subjected to chilling temperatures after cold-acclimation were more tolerant with respect to chlorophyll fluorescence parameters, and Gökçe had better photosystem II (PSII) photochemical activity. In the chilling treatments, total chlorophyll (a + b) content reduced, especially at 2°C, while anthocyanin and flavonoid contents increased to a greater extent in Gökçe and carotenoid content of the cultivars did not change. Malondialdehyde (MDA) content was higher for Can?tez 87, mostly at 2°C, while proline accumulation was greater for Gökçe. The cold-acclimation period led to a remarkable increase in antioxidant enzyme activities of both cultivars. The superoxide dismutase (SOD) activity was much higher in Gökçe for both chilling temperatures and the ascorbate peroxidase (APX) activity increased only in the cold-acclimated 4°C treatments. Similarly, with APX activity, the glutathione reductase (GR) and peroxidase (POD) activities of cultivars were higher in cold-acclimated plants at both the chilling temperatures, mostly in Gökçe. The results of this study indicate that cold-acclimation increased the cultivars ability to withstand the chilling temperatures. The lower MDA content and higher antioxidant and photochemical activities in Gökçe indicated an enhanced chilling tolerance capacity of this cultivar to protect the plant from oxidative damage.     

A novel method for identifying nonlinear gene–environment interactions in case–control association studies

The genetic influences on complex disease traits generally depend on the joint effects of multiple genetic variants, environmental factors, as well as their interplays. Gene × environment (G × E) interactions play vital roles in determining an individual’s disease risk, but the underlying genetic machinery is poorly understood. Traditional analysis assuming linear relationship between genetic and environmental factors, along with their interactions, is commonly pursued under the regression-based framework to examine G × E interactions. This assumption, however, could be violated due to nonlinear responses of genetic variants to environmental stimuli. As an extension to our previous work on continuous traits, we proposed a flexible varying-coefficient model for the detection of nonlinear G × E interaction with binary disease traits. Varying coefficients were approximated by a non-parametric regression function through which one can assess the nonlinear response of genetic factors to environmental changes. A group of statistical tests were proposed to elucidate various mechanisms of G × E interaction. The utility of the proposed method was illustrated via simulation and real data analysis with application to type 2 diabetes.     

Patterns of additive genotype-by-environment interaction in tree height of Norway spruce in southern and central Sweden

Genotype-by-environment (G × E) interaction for tree height measured at ages 7 to 13 was investigated in 20 large open-pollinated progeny trials for Norway spruce (Picea abies (L.) H. Karst.) in southern and central Sweden. Factor analytic method using spatially adjusted data and a reduced animal model was used to explore the pattern of G × E interaction. Extended factor analyses captured 93.0% of additive G × E interaction variances using three factors. The mean daily temperature less than 3.2 °C in May and June explained 27.8% G × E interaction, and it was moderately correlated with the first factor, indicating that spring or autumn frost weather condition could be a main driver for G × E interaction in Norway spruce. Cluster analysis has divided 20 trials into either 6 clusters or 3 clusters. Both sets of clusters reflected the geography of the trials (climates) and the genetic connectedness among testing series, indicating that more trials with better connectedness are required to examine whether current delineation of breeding or seed zones is optimal. Parental stability using latent regression could be used to locate best parents that have the highest breeding values and are highly stable across trials.     

The effects of boron toxicity on root antioxidant systems of two chickpea (Cicer arietinum L.) cultivars

Significant differences in the antioxidant systems of the roots of two chickpea (Cicer arietinum L.) cultivars differing in tolerance to drought were observed in under toxic boron (B) conditions. Three-week-old chickpea seedlings were subjected to 0.05 mM (control), 1.6 mM or 6.4 mM B in the form of boric acid (H₃BO₃) for 7 days. At the end of the treatment period, root length, dry weight, boron concentration, malondialdehyde (MDA) content, and the activities of antioxidant enzymes—superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APOX) and glutathione reductase (GR)—were measured. Root length of the drought-tolerant Gökce cultivar did not change under 1.6 mM B but increased under 6.4 mM B. On the contrary, root length decreased in the drought-sensitive Küsmen cultivar under both B concentrations. While root dry weight was unaffected in Gökce, it decreased in Küsmen under both B concentrations. Boron concentration was significantly higher in Küsmen than in Gökce at both B levels. Significant increases in SOD and POX activities were observed in roots of both cultivars under 1.6 and 6.4 mM B. Root extracts exhibited three SOD and three POX activity bands in both cultivars under B stress when compared to control groups. Although CAT activity in Gökce was increased, it decreased in Küsmen at the highest B concentration as compared to control groups. Roots of both cultivars showed no significant change in APOX activity under B toxicity (except in 1.6 mM B treated roots of Küsmen) when compared to control groups. GR activity in the roots of Küsmen decreased significantly with increasing B concentration. However, a significant increase in GR activity was found in Gökce under 1.6 mM B stress. In addition, lipid peroxidation levels of drought-sensitive Küsmen increased, indicating more damage to membrane lipids due to B toxicity. Lipid peroxidation did not change in the drought-tolerant Gökce cultivar at either B concentration. These results suggest that roots of Gökce are better protected from B-stress-induced oxidative stress due to enhanced SOD, CAT and POX activities under high B levels.     

Discrimination of American Cranberry Cultivars and Assessment of Clonal Heterogeneity Using Microsatellite Markers

Cranberries (Vaccinium macrocarpon Ait.) are an economically important fruit crop derived from a North American native species. We report the application of 12 simple sequence repeats (SSR) or microsatellite markers to assess the genetic diversity of cranberry cultivars. We studied 164 samples of 21 different cranberry cultivars, 11 experimental hybrids, and 6 representative accessions of wild species. Genetic cluster analysis, based on 117 SSR alleles, differentiated the major cranberry cultivars. However, some cranberry cultivar subclone variants and mislabeled samples were observed. Consensus genetic profiles identified the most likely clonal representatives of several important cranberry cultivars (e.g., “Ben Lear,” “Howes,” and “Stevens”). The markers were further used to confirm putative parents of several hybrid progenies. The long-term goal of our studies is to identify, preserve, and utilize unique genetic materials to breed improved cranberries. Attaining this goal will help growers maintain sustainability under changing economic and environmental conditions.     

Construction of fingerprinting for tea plant (<Emphasis Type="Italic">Camellia sinensis</Emphasis>) accessions using new genomic SSR markers

As one of the most popular non-alcoholic beverage crops, the tea plant (Camellia sinensis) plays an important role in human health and lifestyle. Genetic fingerprinting based on genomic-derived markers in tea, however, is still in the initial stages, which has limited tea germplasm resource utilization and cultivar protection. In the current study, we identified whole genome-based simple sequence repeat (SSR) loci and successfully developed 36 new genomic SSR markers, which are highly polymorphic with average allele number and polymorphic information content (PIC) of 14.9 and 0.862, respectively. A phylogenetic tree for 80 tea plant accessions was subsequently constructed based on their genotypic scores for these 36 markers. The phylogenetic relationships among the 80 accessions are highly consistent with their genetic backgrounds or original places. Noteworthy, robust fingerprinting power was performed, and the overall probability of finding two random individuals sharing identical genotypes across the 36 loci was estimated to be 1.5 × 10^?56. We subsequently identified five SSR markers as a recommended core marker set for fingerprinting the tea plant cultivars or accessions. The combined PI and PIsibs of the marker set were 1.49 × 10^?9 and 2.57 × 10^?3, respectively, which allowed us to fully discriminate all 80 tea plant accessions from one another. The SSR markers developed here will provide a valuable resource for tea plant genetics and genomic studies, as well as breeding programs. The fingerprinting profiles can serve as a database that is essential for the tea industry and commercial breeding, and for tea plant cultivar identification, utilization, and protection.     

Polymorphism of microsatellite loci in cultivars and species of pear (<Emphasis Type="Italic">Pyrus</Emphasis> L.)

Using five SSR markers, polymorphism of microsatellite loci was examined in 46 cultivars and five species of pear (Pyrus ussuriensis, P. bretscgneideri, P. pyraster, and P. elaegnifolia). Most of the accessions examined showed the presence of unique allele sets. The degree of relationship between Russian and Western European pear cultivar was established. It was demonstrated that P. ussuriensis and its first generation progeny were genetically distant from typical cultivars of P. communis, as well as from the P. communis × P. ussuriensis hybrids of later generations. SSR estimates of the cultivar relatedness were shown to correlate with the corresponding pedigree-based estimates. A number of SSR alleles specific to P. ussuriensis were identified. Based on the analysis of microsatellite loci, the allelic composition was determined for each cultivar examined. These data can serve as a molecular certificate of the cultivar.     

Population genetics of Scirtothrips perseae: tracing the origin of a recently introduced exotic pest of Californian avocado orchards, using mitochondrial and microsatellite DNA markers

The Californian avocado industry has recently been impacted by the establishment of three exotic arthropod pests that are native to Mexico and Central America. Establishment of all three pests is thought to have resulted from illegal movement of host plants (avocado) into California. To identify likely sources and routes of entry of such pest invasions, we examined the population genetics of the most recent invader, avocado thrips [Scirtothrips perseae Nakahara (Thysanoptera: Thripidae)], using mitochondrial DNA (mtDNA) and microsatellite markers. The mtDNA sequences revealed three geographically distinct and divergent lineages, of which the mtDNA haplotypes of Californian individuals were most closely related to populations in the center of the pest's native range. Analysis of allele frequencies at four microsatellite loci added resolution, indicating Coatepec Harinas, Mexico, as the most likely source of the Californian population. Statistically, we did not detect any bottleneck in population size associated with the invasion of California. However, estimates of the effective population size of the invading population suggest that a severe bottleneck occurred, indicating that the quantity of host‐plant material entering California was small. Our findings implicate Coatepec Harinas, a large avocado germplasm and breeding center, as the most likely source of the introduced Californian population of S. perseae and as a likely source of previous and future avocado pest introductions. Efforts to identify natural enemies of S. perseae for biological control should focus on Coatepec Harinas and immediate surrounds. Moreover, identification of the source of invasive pests enables the establishment and enforcement of plant quarantine and free‐trade protocols.